5W50 or 10W50 oil ??

have recently changed the oil on the blue baron to mobil 1 0W40 after 1500 miles on 0W40 semi synth after a rebuild. it seems to be a little smokey on start up after its been sat for a while so maybe the oil is getting through the heads as its common on the flat 6 I am told. i think the engine needs some more running in as its only been 1500 miles am thinking its too thin and have been advised to look at a 5W50 or 10W50 fully synth oil like the Millers. is anyone else running this oil and find it better than 0w40? is it the case that 0w40 is a lot thinner when its cold hence the 0 setting and its not as effective when hot as a 50? thanks

A 0W is thinner when cold than a 10W. Its still a shed load thicker when cold than any other engine oil is when warm tho.

As seen on your pressure gauge.

Unless you are intending for it to see some track action there is not much point putting xW50 oil in. 5w40 FS should be fine, I know hartech put 10w40 in their rebuild engines, but this has always seemed odd to me. I would have thought the 5w40 should resolve the smoking,

I wouldn't put a 0w oil anywhere near a car with a few miles on. The only purpose such a thin oil serves to to reduce startup emissions. I run a Millers 10w40 on my 130k+ 996 as many engine specialists suggest. I have very short drain periods (6k miles max). Asking for oil advice on the internet is opening a can of worms.

I've just switched to 10/50 millers. Summer car, occasional use so high temp viscosity is more important to me than cold start. Gauge now reads 0.5 bar higher when idling, hot. As said, it's all a can of worms, but I'm happy with the higher temp protection.

I used to get a puff of smoke on startup from mine, I tried 10W40 and it didn't help, and then I had a catastrophic AOS failure. Once the AOS had been replaced with a new one, the smoke on startup thing went away. Did you replace yours as part of your rebuild?

I thought his too although I don't know how it works, I would have thought the thinner oil would produce more oil burning on startup (smoke etc)?

Use mine daily all year for 4 years now + summer eurotrips. 123K miles on mobil 1 0w50 from day 1. Uses about 1 litre per 10k miles. Long way before I catch poppopbangbang at quarter of a million miles on mobil 1. Not saying its right..........but if it ain't broke...... :dont know: My mate's logic is thinner when cold circulates everywhere quicker on start up and prevent less initial wear. Who knows? :dont know:

I am not sure to be honest martin so will check AOS - is that the air oil separator?

.. makes sense. I have continued using Mobil Super 3000 5w/40 which 'seems' fine. Was a little concerned about consumption early on in ownership - but I think that's just me being paranoid as not really had any issues since. Full pressure on the gauge and engine sounds again fine from cold start Plan to change twice yearly for the sake of it. 88k on mine, not my daily :thumb:

Yes.....and if its worn will allow oil to get into the air intake. So then may show as a smoky start-up.

The thinner oil is great when engines are new - as you say it gets everywhere quick, and reduces friction. The manufacturer loves it because less friction = more efficiency = lower emissions. But on a worn engine with wider tolerances does it provide a useful film to prevent wear? I wonder if you used 5w40 oil would your car consume less oil? However as you say perhaps if it ain't broke, don't fix it, and that consumption is within handbook tolerance. I'm not an oil or even an engine expert and most forum users aren't either, thats why theres so many arguments.

I'm on the fence and have been since hitting 100k. If I had a 3.6 I'd deffo be on thicker, but I've seen too many high miler 3.4s that folk have run on mobil 1 to sway me to the dark side.

AOS went on my 4S. Frightened me to death, engine made a ghastly screeching noise (apparently air being sucked in through a small gap). A cheap £80 part, but requires the engine to be dropped to fix, though some models can be done in situ. So over £1k for some pointless bit. So well worth doing if you have the engine down for some other reason. But yes, oil consumption had increased quite a lot beforehand.